The present invention relates to an aqueous ink composition suitable for use as printing ink and stamping ink in general use, and for use with writing instruments, recording apparatus or the like. More particularly, it relates to an aqueous black ink composition for ink-jet printing, which is capable of yielding printed images with high quality (i.e., high clearness and sharpness, etc.), and with excellent resistance to water and light, and which is also capable of providing stable ink ejection, without causing the plugging of the nozzles of the ink-jet printing apparatus, even if it is used continuously for a long period of time or it is used intermittently after a period of non-use of the ink-jet printing apparatus.
As the dyes for use in the conventional black aqueous inks, for example, direct dyes such as C.I. Direct Black -2, -4, -17, -19, -22, -33, -38, -51, -56, -62, -71, -74, -75, -77, -105, -108, -112 and -154; and acid dyes such as C.I. Acid Black -1, -2, -7, -24 and -94 are employed in practice.
Of the above-mentioned dyes for the conventional aqueous inks, the solubility of the direct dyes in the solvent of the aqueous inks is so low that the content of the dye in the inks cannot be increased. The result is that the inks cannot provide images having high density and high contrast. Furthermore, even if the concentration of the direct dye in the inks is held down, the dye precipitates from the inks during an extend period of storage, or during the periods when the ink-jet printing apparatus is not in use. As a result, the nozzles are plugged with the precipitates and it becomes impossible to obtain the desired ink ejection stability and the desired ink ejection response.
The conventional acid dyes have a higher solubility in the solvent of the aqueous inks as compared with the above-mentioned direct dyes. However, images printed by the aqueous inks employing the conventional acid dyes are not resistant to water and exposure to light and therefore are poor in preservability.